André de Lustrac

Electronic control of linear-to-circular polarization conversion using a reconfigurable metasurface

A reflective metasurface enabling linear-to-circular polarization (LP-to-CP) conversion is proposed. The metasurface polarizer is composed of active unit cells incorporating voltage-controlled varactor diodes, where the dispersion responses of the cells can be tailored. When illuminated by an incident wave, the metasurface converts the LP wave from the source to a CP one. Moreover, in a single voltage configuration, two circular polarized waves with different handedness can be obtained at distinct frequencies. Such operation can be tuned in frequency by changing the applied voltage along the metasurface. Simulations are performed to verify the concept, and measurements done on a fabricated prototype validate the polarization conversion performances at microwave frequencies.

Direct dark modes excitation in bi-layered enantiomeric atoms-based metasurface through symmetry matching.

We provide evidence for the mechanism of direct dark mode excitation in a metasurface composed of bi-layered Z-shaped enantiomeric meta-atoms. The electromagnetic behavior of the structure is investigated through both numerical simulations and experimental measurements in the microwave domain. We demonstrate direct field coupling excitation of second higher order electric mode under normal incidence based only on symmetry matching conditions. The proposed approach provides a better flexibility in engineering dark mode resonances that do not rely on hybridization mechanism and presents important advantages for multi-spectral sensor applications.

Guided wave metamaterials for integrated optics applications

This work addresses analysis of hybrid plasmonic/dielectric metamaterials operated in guided wave configurations in the near-infrared domain (» = 1.5 µm). The objective is to achieve an efficient control over the flow of the light in the waveguide using effective index variation induced by metasurface resonances. Specifically we consider a composite guiding structure made of a 2D plasmonic metasurface located on the top of high index silicon on insulator waveguide. The great advantages of the considered solution with respect to the conventional multilayered metamaterials approach are simplified technology and reduced propagation losses. In contrast to photonic crystals approach, the use of plasmonic nanoresonators allows a much higher degree of freedom for the control of effective index. Depending on the operation with respect to the resonance frequency, effective index either higher or lower as that of the host slab waveguide can be achieved. The considered approach is quite generic and can be adapted to different type of planar lightwave circuits platforms: Silicon, GaN/AlN, InGaAsP/InP, doped silica glass etc. The reported demonstrations opens thus the way to a new family of optical devices based on the use of plasmonic resonances to control the light at nanoscale.